Hepatitis is caused by viruses. Several types of hepatitis viruses have been identified. Among them, hepatitis A and B viruses are the most common. Four other known hepatitis viruses are designated as hepatitis C, D, E, and G. Hepatitis A and E viruses only cause acute infection, while hepatitis B and C are chronic illness. Hepatitis D virus is only present in patients co-infected with hepatitis B. However, the etiology of a substantial number of patients with acute and chronic hepatitis remains unknown. Thus, identification of additional causative agents is needed.